In conventional papermaking machines, wet felts convey the sheet of paper, paperboard, etc., from the wire or cylindrical mold thrugh various water removing equipment.
Such wet felts are often woven endless and are applied as such to the rolls of the papermaking machine. The installation of endless wet felts in the past has required cessation of operations for extended periods of time with the resultant loss of production from the paper machine.
Recent developments have resulted in greater use of seamed press felts which are joined or seamed by a pintle to simulate the endless condition. This construction is generally described as a pintle seamed joint. The inability to produce a pintle seamed joint geometry which does not differ substantially from the plane of the fabric body has been a major fault with this newer construction.
In view of the prior failures, the present invention teaches the use of an extended loop in the seam area. Although this is occasionally contrary to the prior art theory of continuing the same weave or float length through the fabric seam area, the invention permits greater control over the seam configuration and, in fact, results in a more uniform fabric geometry at the seam.
U.S. Pat. 2,883,734 provided a wet felt of a woven open-ended strip construction which was made endless by joining together the extensions of yarn from the weave of the felt at the joining ends thereof. One end of the wet felt is fed through the dryer section of the machine, until it completes a full loop. The yarn extensions at the joining ends of the felt are continuous with the weave system thereof and are used for joining together the two ends of the felt, and a textile yarn or cord is used to secure both sets of yarn extensions together and retain the two ends of the felt connected together to form an endless belt structure. Thus, the wet felt is installed without having to disassemble the machine.
The art is replete with descriptions of seam constructions for papermakers felts; see for example the disclosures of U.S. Pat. Nos. 2,883,734; 3,283,388; 3,309,790; 4,123,022; 4,141,388; 4,186,780 and 4,364,421. In general, the seam constructions of the prior art have not been entirely satisfactory for all purposes and applications.
U.S. Pat. No. 4,500,590 issued Feb. 19, 1985 to Smith, attempts to solve this problem via a composite pintle including a polyester core and an outer low-melt polymeric sheath which has been softened and deformed. This composite pintle exhibits a profile which occupies void areas in the mesh of the helical fabric in the area of the pintle joint.
The difficulty in establishing overall uniformity between the caliper of the fabric and the caliper of the seam has been recognized in the prior art. Likewise, it has been recognized, in the prior art, that the normal construction of a single layer fabric results in a fabric thickness which is less than three times the yarn diameters, due to the crimp introduced into the yarns and a seam thickness which is about three yarn diameters. For example, a single layer fabric of normal construction, having monofilament warp threads and weft threads, would typically have a thickness which is only two and a half times the yarn diameter, rather than three times the yarn diameter as may be expected. This condition is discussed in detail in U.S. Pat. No. 4,026,331 which is incorporated herein by reference as if fully set forth. As recognized in U.S. Pat. No. 4,026,331, one approach to controlling equality between seam thickness and fabric thickness is to select certain weaves and cover factors which will permit equalization and uniformity of overall fabric caliper. However, such an approach eliminates many desirable weave constructions and fabrics which do not have the requisite percentage of warp cover or met the weave limitations. Accordingly, the present invention sets forth a structure which will accomplish the goals of U.S. Pat. No. 4,026,331 without the inherit limitations thereof.